ADEN (Reuters) - A bomb next to the governor’s office in the Yemeni city of Aden killed four people on Thursday, witnesses said, and the European Union urged parties to avoid hitting civilian infrastructure after Saudi-led air strikes on Hodeida port.

No one claimed responsibility for the blast in the main southern port city of Aden, which is controlled by forces allied with exiled President Abd-Rabbu Mansour Hadi, after they drove the Houthis out last month. An official said the governor was present but unhurt.

Hundreds of kilometers away in the Empty Quarter desert, a local official said unknown gunmen attacked a government military post in the Thamud district near Saudi Arabia, killing four soldiers.

In a statement posted online, the Islamic State militant group said it carried out the assault on the “apostate army,” its first known attack against the government since it emerged this year.

The attacks underscore the fragility of Yemen’s government despite hundreds of air strikes from Saudi-led Arab states. That campaign has helped Hadi’s government win control over most of southern Yemen and reversed the gains of the Houthis, an Iran-allied group, after five months of civil war.

Plagued by chronic instability even before the latest civil war, Yemen is also home to the world’s deadliest branch of al Qaeda and a new offshoot of Islamic State.

The attacks hit five provinces controlled by the Houthis and the military airport in Sanaa amid rapid advances by Arab-backed Yemeni troops.

The attacks came on the heels of air raids on Yemen’s Red Sea port of Hodeida on Tuesday, which officials there said had destroyed cranes and warehouses in the main entry point for aid supplies to the north of the country.

The EU condemned the attacks.

“The recent airstrikes and shelling of Hodeida port facilities have created an additional and immediate obstacle to the import of food, fuel, medicines and other critical goods to alleviate some of the most pressing needs of the population,” said a joint statement by the spokespersons of EU foreign policy chief, Federica Mogherini, and Humanitarian Aid and Crisis Management coordinator Christos Stylianides.

“The EU calls on all parties to the conflict to refrain from deliberately targeting civilian infrastructure.”

“SENSELESS BLOODSHED”

The Saudi-led alliance began its air strikes in late March as the Shi’ite Houthis entered Aden. The civil war has killed over 4,300 people and left diplomats and air groups appealing for a ceasefire to spare civilians and alleviate a mounting humanitarian disaster.

One air raid on a school in Amran province north of Sanaa on Tuesday killed 13 teachers and four children, in an attack the United Nations called “senseless bloodshed.”

“No nation, no society, can afford to lose its children to conflict - whether from direct attacks, from malnutrition, from disease, from lack of education, or from the traumas of the horrors they witness,” U.N. agency UNICEF said in a statement. It noted around eight children have been killed or wounded in the war every day.

Sunni Arab countries and Yemen’s Saudi-based government see the Houthis as a proxy of Shi’ite Iran, bent on extending the Islamic Republic’s influence in the Arab world.

The Houthis and Iran deny this. The Houthis see their move as a revolution against corrupt officials and claim they are fighting Islamist hardliners linked to al Qaeda.

Southern Yemeni militias and loyalist army units have scored major gains against the Houthis in the last month and may soon advance toward their stronghold around Sanaa.

But as a political accord remains elusive, suffering and hunger continue to spread.

Ertharin Cousin, the head of the U.N.’s World Food Program, warned after a three-day visit to the country that the violence and near-blockade by Arab forces may push already widespread hunger out of control.

“Ten of the 22 governorates in Yemen in July were already at emergency levels. That’s one step away from famine.”

Additional reporting by Shadi Bushra in Cairo and Alastair Macdonald in Brussels,; Writing by Noor Chehayber and Sami Aboudi,; Editing by Dominic Evans and Toby Chopra